Circular hole cutters such as the tool described in U.S. Pat. No. 3,146,675 issued Sep. 1, 1964, to Anderson utilize a side cutting milling bit rotatably driven by a source of rotational torque such as a portable electric drill, to cut a circular holes of varying sizes in materials such as sheet steel. The milling or cutting bit of such a tool is guided in a circular path about a radius point by a support frame which has mounted thereon in compass fashion the bit and the radius point. It is desireable that such circular hole cutters include an elongated support frame so that the radius point may be adjustably mounted along its length, allowing circular holes having a wide range of diameters to be cut by the hole cutter. It is also desireable that such a circular hole cutter have a control handle extending forwardly from its forward end to better control the tool as cutting progresses. However, any extension of the length of such a hole cutter introduces limitations on areas in which the hole cutter may be utilized. For example, where an elongated hole cutter has its radius point adjusted to allow the hole cutter to cut a small hole, the framework of the hole cutter extending rearward of the radius point may come into obstructive contact with nearby walls, pipes or other obstacles near the desired hole. Also, a handle element protruding forwardly from such a hole cutter may prevent the hole cutter from being utilized to cut holes in close proximity to an obstruction such as a wall or a ceiling. Thus, it is desireable to construct a circular hole cutter which may be configured as a long span, forward handle assisted, cutter for cutting large diameter holes with the assistance of a forward protruding handle, and alternately configured as a short span cutter having no forward handle, for cutting holes in tight spaces.
It is also often desireable to cut circular holes in stratified materials such as sound insulated sheet metal having a layer of sound insulating material underlying the sheet metal. A rotatably driven side cutting milling bit is ideally suited for cutting the top layer of sheet metal. However, a milling bit may be an inefficient means of cutting the underlying insulation. Typically, the cutting action of a knife blade is a better means of cutting such underlying insulation. Where such stratified material is to be cut by a rotatably driven milling bit guided in a circular path by a hole cutting tool, it is desireable that the tool provide for mounting of and simultaneous guiding of a cutting blade, such blade being capable of cutting at a depth deeper than and along the same circular path as the milling bit.
The instant inventive circular hole cutting tool provides the desireable trait of alternate long and short configurations, utilizing forward telescoping and retracting handle a rearward telescoping and retracting radius arm; and the desireable trait of a cutting blade mounting means for simultaneous blade cutting and milling bit cutting of stratified materials.